Method and device for electromagnetic cooking using non-centered loads management through spectromodal axis rotation

ABSTRACT

An electromagnetic cooking device includes a cavity in which a food load is placed, a plurality of RF feeds for introducing electromagnetic radiation into the enclosed cavity, and a controller configured to detect asymmetries and select rotations that compensate for the asymmetries; select a heating target including a plurality of resonant modes that are rotated using the selected rotations in the preceding step; generate a heating strategy based on the heating target to determine a sequence of desired heating patterns; cause the RF feeds to output a radio frequency signal to thereby excite the enclosed cavity with a selected set of phasors for a set of frequencies; and monitor the created heating patterns based on the forward and backward power measurements at the RF feeds to use closed-loop regulation to selectively modify the sequence of resonant modes into the enclosed cavity based on the desired heating patterns as monitored.

BACKGROUND

The present device generally relates to a method and device forelectromagnetic cooking, and more specifically, to a method and devicefor determining and controlling the resonant modes within a microwaveoven.

A conventional microwave oven cooks food by a process of dielectricheating in which a high-frequency alternating electromagnetic field isdistributed throughout an enclosed cavity. A sub-band of the radiofrequency spectrum, microwave frequencies at or around 2.45 GHz causedielectric heating primarily by absorption of energy in water.

To generate microwave frequency radiation in a conventional microwave, avoltage applied to a high-voltage transformer results in a high-voltagepower that is applied to a magnetron that generates microwave frequencyradiation. The microwaves are then transmitted to an enclosed cavitycontaining the food through a waveguide. Cooking food in an enclosedcavity with a single, non-coherent source like a magnetron can result innon-uniform heating of the food. To more evenly heat food, microwaveovens include, among other things, mechanical solutions such as amicrowave stirrer and a turntable for rotating the food. A commonmagnetron-based microwave source is not narrowband and not tunable (i.e.emits microwaves at a frequency that is changing over time and notselectable). As an alternative to such a common magnetron-basedmicrowave source, solid-state sources can be included in microwave ovenswhich are tunable and coherent.

SUMMARY

In one aspect, an electromagnetic cooking device includes an enclosedcavity in which a food load is placed; a plurality of RF feedsconfigured to introduce electromagnetic radiation into the enclosedcavity to heat up and prepare the food load, the plurality of RF feedsconfigured to allow measurement of forward and backward power at theplurality of RF feeds; and a controller configured to: detectasymmetries relative to a center of the enclosed cavity and selectrotations that compensate for the detected asymmetries; select a heatingtarget corresponding to an amount of energy that is to be to deliveredto each symmetry plane in the enclosed cavity based in part upon thefood load positioned in the enclosed cavity where the heating targetincludes a plurality of resonant modes that are rotated using theselected rotations in the preceding step; generate a heating strategybased on the heating target to determine a sequence of desired heatingpatterns, the heating strategy having a selected sequence of theplurality of resonant modes to be excited in the enclosed cavity thatcorresponds to the sequence of desired heating patterns; cause the RFfeeds to output a radio frequency signal of a selected frequency, aselected phase value and a selected power level to thereby excite theenclosed cavity with a selected set of phasors for a set of frequenciescorresponding to each resonant mode of the selected sequence of resonantmodes to create heating patterns; and monitor the created heatingpatterns based on the forward and backward power measurements at the RFfeeds to use closed-loop regulation to selectively modify the sequenceof resonant modes into the enclosed cavity based on the desired heatingpatterns as monitored.

In another aspect, a method of activating a sequence of preclassifiedresonant modes into an enclosed cavity in which a food load is placed tocontrol a heating pattern therein with RF radiation from a plurality ofRF feeds, where the plurality of RF feeds transfer the RF radiation intothe enclosed cavity and measure the forward and backward power at theplurality of RF feeds, the method comprising: detecting asymmetriesrelative to a center of the enclosed cavity and select rotations thatcompensate for the detected asymmetries; selecting a heating targetcorresponding to an amount of energy that is to be to delivered to eachsymmetry plane in the enclosed cavity based in part upon the food loadpositioned in the enclosed cavity where the heating target includes aplurality of resonant modes that are rotated using the selectedrotations in the preceding step; generating a heating strategy based onthe heating target and the selected rotations to determine a sequence ofdesired heating patterns, the heating strategy having a selectedsequence of the plurality of optimized resonant modes to be excited inthe enclosed cavity that corresponds to the sequence of desired heatingpatterns; exciting the enclosed cavity with a selected set of phasorsfor a set of frequencies corresponding to each resonant mode of theselected sequence of optimized resonant modes to create heatingpatterns; and monitoring the created heating patterns based on theforward and backward power measurements at the RF feeds to useclosed-loop regulation to selectively modify the sequence of optimizedresonant modes into the enclosed cavity based on the desired heatingpatterns as monitored.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a block diagram of an electromagnetic cooking device withmultiple coherent radio frequency feeds in accordance with variousaspects described herein.

FIG. 2 is a block diagram of a radio frequency signal generator of FIG.1.

FIG. 3 is a schematic diagram illustrating a high-power radio frequencyamplifier coupled to a waveguide in accordance with various aspectsdescribed herein.

FIG. 4 is a cross-sectional diagram illustrating an integratedcirculator for use in a high-power radio frequency amplifier inaccordance with various aspects described herein.

FIG. 5 is a top-view diagram illustrating the integrated circulator ofFIG. 4.

FIG. 6 is a schematic diagram illustrating a high-power radio frequencyamplifier coupled to a waveguide with an integrated measurement systemin accordance with various aspects described herein.

FIG. 7 is a schematic diagram illustrating a high-power radio frequencyamplifier coupled to a waveguide with an integrated measurement systemincluding a reflectometer in accordance with various aspects describedherein.

FIG. 8 is a schematic diagram illustrating a resonant cavity coupled totwo radio frequency waveguides in accordance with various aspectsdescribed herein.

FIG. 9 is a graphical diagram illustrating efficiency versus frequencyfor in-phase and antiphase excitations of the resonant cavity of FIG. 8.

FIG. 10 is a diagram illustrating features of a method of analysis todetermine the resonant modes of the cavity in accordance with variousaspects described herein.

FIG. 11 is a diagram illustrating features of a method to characterizethe resonant modes of the cavity in accordance with various aspectsdescribed herein.

FIGS. 12A and 12B are schematic diagrams illustrating features of amethod to locate and classify foodstuff positioned within a resonantcavity in accordance with various aspects described herein.

FIG. 13 is a graphical diagram illustrating efficiency versus frequencyfor in-phase excitations of the resonant cavity of FIG. 8 showing the Qfactors.

FIG. 14 is a diagram illustrating features of a method to characterizethe unbalanced resonant modes of the cavity in accordance with variousaspects described herein.

FIG. 15 is a diagram illustrating features of a method to characterizethe balanced resonant modes of the cavity in accordance with variousaspects described herein.

FIG. 16 is a flowchart illustrating a method of exciting an enclosedcavity with radio frequency radiation in accordance with various aspectsdescribed herein.

FIG. 17 is a diagram illustrating features of a method to characterizethe unbalanced resonant modes of the cavity when a non-centered foodload is present in accordance with various aspects described herein.

FIG. 18 is a diagram illustrating features of a method to characterizethe balanced resonant modes of the cavity when a non-centered food loadis present in accordance with various aspects described herein.

FIG. 19 are plots of the phase vs efficiency curves of one example fortwo symmetries.

FIG. 20 are plots of the phase vs efficiency curves of another examplefor two symmetries.

FIG. 21 is a block diagram illustrating an open-loop regulation of aheating strategy synthesis.

FIG. 22 is a block diagram illustrating a closed-loop regulation of aheating strategy synthesis.

FIG. 23A is an efficiency map of one example of a food load in theenclosed cavity where the cooking appliance includes two ports.

FIG. 23B is an efficiency map of one example of a food load in theenclosed cavity where the cooking appliance includes four ports.

FIG. 24A is an efficiency map of an example where the system is mostlysymmetric and most of the resonances are not rotated.

FIG. 24B is an efficiency map of an example where the system is mostlyasymmetric and most of the resonances are rotated.

FIG. 25 is a flowchart illustrating an alternative method of exciting anenclosed cavity with radio frequency radiation in accordance withvarious aspects described herein.

DETAILED DESCRIPTION

It is to be understood that the specific devices and processesillustrated in the attached drawings, and described in the followingspecification are simply exemplary embodiments of the inventive conceptsdefined in the appended claims. Hence, other physical characteristicsrelating to the embodiments disclosed herein are not to be considered aslimiting, unless the claims expressly state otherwise.

A solid-state radio frequency (RF) cooking appliance heats up andprepares food by introducing electromagnetic radiation into an enclosedcavity. Multiple RF feeds at different locations in the enclosed cavityproduce dynamic electromagnetic wave patterns as they radiate. Tocontrol and shape of the wave patterns in the enclosed cavity, themultiple RF feeds can radiate waves with separately controlledelectromagnetic characteristics to maintain coherence (that is, astationary interference pattern) within the enclosed cavity. Forexample, each RF feed can transmit a different frequency, phase and/oramplitude with respect to the other feeds. Other electromagneticcharacteristics can be common among the RF feeds. For example, each RFfeed can transmit at a common but variable frequency. Although thefollowing embodiments are directed to a cooking appliance where RF feedsdirect electromagnetic radiation to heat an object in an enclosedcavity, it will be understood that the methods described herein and theinventive concepts derived therefrom are not so limited. The coveredconcepts and methods are applicable to any RF device whereelectromagnetic radiation is directed to an enclosed cavity to act on anobject inside the cavity. Exemplary devices include ovens, dryers,steamers, and the like.

FIG. 1 shows a block diagram of an electromagnetic cooking device 10with multiple coherent RF feeds 26A-D according to one embodiment. Asshown in FIG. 1, the electromagnetic cooking device 10 includes a powersupply 12, a controller 14, an RF signal generator 16, a human-machineinterface 28 and multiple high-power RF amplifiers 18A-D coupled to themultiple RF feeds 26A-D. The multiple RF feeds 26A-D each transfer RFpower from one of the multiple high-power RF amplifiers 18A-D into anenclosed cavity 20.

The power supply 12 provides electrical power derived from mainselectricity to the controller 14, the RF signal generator 16, thehuman-machine interface 28 and the multiple high-power RF amplifiers18A-D. The power supply 12 converts the mains electricity to therequired power level of each of the devices it powers. The power supply12 can deliver a variable output voltage level. For example, the powersupply 12 can output a voltage level selectively controlled in 0.5-Voltsteps. In this way, the power supply 12 can be configured to typicallysupply 28 Volts direct current to each of the high-power RF amplifiers18A-D, but can supply a lower voltage, such as 15 Volts direct current,to decrease an RF output power level by a desired level.

A controller 14 can be included in the electromagnetic cooking device10, which can be operably coupled with various components of theelectromagnetic cooking device 10 to implement a cooking cycle. Thecontroller 14 can also be operably coupled with a control panel orhuman-machine interface 28 for receiving user-selected inputs andcommunicating information to a user. The human-machine interface 28 caninclude operational controls such as dials, lights, switches, touchscreen elements, and displays enabling a user to input commands, such asa cooking cycle, to the controller 14 and receive information. The userinterface 28 can include one or more elements, which can be centralisedor dispersed relative to each other. The controller 14 may also selectthe voltage level supplied by power supply 12.

The controller 14 can be provided with a memory and a central processingunit (CPU), and can be preferably embodied in a microcontroller. Thememory can be used for storing control software that can be executed bythe CPU in completing a cooking cycle. For example, the memory can storeone or more pre-programmed cooking cycles that can be selected by a userand completed by the electromagnetic cooking device 10. The controller14 can also receive input from one or more sensors. Non-limitingexamples of sensors that can be communicably coupled with the controller14 include peak level detectors known in the art of RF engineering formeasuring RP power levels and temperature sensors for measuring thetemperature of the enclosed cavity or one or more of the high-poweramplifiers 18A-D.

Based on the user input provided by the human-machine interface 28 anddata including the forward and backward (or reflected) power magnitudescoming from the multiple high-power amplifiers 18A-D (represented inFIG. 1 by the path from each of the high-power amplifiers 18A-D throughthe RF signal generator 16 to the controller 14), the controller 14 candetermine the cooking strategy and calculate the settings for the RFsignal generator 16. In this way, one of the main functions of thecontroller 14 is to actuate the electromagnetic cooking device 10 toinstantiate the cooking cycle as initiated by the user. The RF signalgenerator 16 as described below then can generate multiple RF waveforms,that is, one for each high-power amplifier 18A-D based on the settingsindicated by the controller 14.

The high-power amplifiers 18A-D, each coupled to one of the RF feeds26A-D, each output a high power RF signal based on a low power RF signalprovided by the RF signal generator 16. The low power RE signal input toeach of the high-power amplifiers 18A-D can be amplified by transformingthe direct current electrical power provided by the power supply 12 intoa high power radio frequency signal. In one non-limiting example, eachhigh-power amplifier 18A-D can be configured to output an RF signalranging from 50 to 250 Watts. The maximum output wattage for eachhigh-power amplifier can be more or less than 250 Watts depending uponthe implementation. Each high-power amplifier 18A-D can include a dummyload to absorb excessive RF reflections.

The multiple RF feeds 26A-D transfer power from the multiple high-powerRF amplifiers 18A-D to the enclosed cavity 20. The multiple RF feeds26A-D can be coupled to the enclosed cavity 20 in spatially separatedbut fixed physical locations. The multiple RF feeds 26A-D can beimplemented via waveguide structures designed for low power losspropagation of RF signals. In one non-limiting example, metallic,rectangular waveguides known in microwave engineering are capable ofguiding RF power from a high-power amplifier 18A-D to the enclosedcavity 20 with a power attenuation of approximately 0.03 decibels permeter.

Additionally, each of the RF feeds 26A-D can include a sensingcapability to measure the magnitude of the forward and the backwardpower levels or phase at the amplifier output. The measured backwardpower indicates a power level returned to the high-power amplifier 18A-Das a result of an impedance mismatch between the high-power amplifier18A-D and the enclosed cavity 20. Besides providing feedback to thecontroller 14 and the RF signal generator 16 to implement, in part, acooking strategy, the backward power level can indicate excess reflectedpower that can damage the high-power amplifier 18A-D.

Along with the determination of the backward power level at each of thehigh-power amplifiers 18A-D, temperature sensing at the high-poweramplifier 18A-D, including at the dummy load, can provide the datanecessary to determine if the backward power level has exceeded apredetermined threshold. If the threshold is exceeded, any of thecontrolling elements in the RF transmission chain including the powersupply 12, controller 14, the RF signal generator 16, or the high-poweramplifier 18A-D can determine that the high-power amplifier 18A-D can beswitched to a lower power level or completely turned off. For example,each high-power amplifier 18A-D can switch itself off automatically ifthe backward power level or sensed temperature is too high for severalmilliseconds. Alternatively, the power supply 12 can cut the directcurrent power supplied to the high-power amplifier 18A-D.

The enclosed cavity 20 can selectively include subcavities 22A-B byinsertion of an optional divider 24 therein. The enclosed cavity 20 caninclude, on at least one side, a shielded door to allow user access tothe interior of the enclosed cavity 20 for placement and retrieval offood or the optional divider 24.

The transmitted bandwidth of each of the RF feeds 26A-D can includefrequencies ranging from 2.4 GHz to 2.5 GHz. The RF feeds 26A-D cart beconfigured to transmit other RF bands. For example, the bandwidth offrequencies between 2.4 GHz and 2.5 GHz is one of several bands thatmake up the industrial, scientific and medical (ISM) radio bands. Thetransmission of other RI bands is contemplated and can includenon-limiting examples contained in the ISM bands defined by thefrequencies: 13.553 MHz to 13.567 MHz, 26.957 MHz to 27.281 MHz, 902 MHzto 928 MHz, 5.725 GHz to 5.875 GHz and 24 GHz to 24.250 GHz.

Referring now to FIG. 2, a block diagram of the RI signal generator 16is shown. The RF signal generator 16 includes a frequency generator 30,a phase generator 34 and an amplitude generator 38 sequentially coupledand all under the direction of an RF controller 32. In this way, theactual frequency, phases and amplitudes to be output from the RF signalgenerator 16 to the high-power amplifiers are programmable through theRI controller 32, preferably implemented as a digital control interface.The RF signal generator 16 can be physically separate from the cookingcontroller 14 or can be physically mounted onto or integrated into thecontroller 14. The RF signal generator 16 is preferably implemented as abespoke integrated circuit.

As shown in FIG. 2 the RF signal generator 16 outputs four RI channels40A-D that share a common but variable frequency (e.g. ranging from 2.4GHz to 2.5 GHz), but are settable in phase and amplitude for each RIchannel 40A-D. The configuration described herein is exemplary andshould not be considered limiting. For example, the RF signal generator16 can be configured to output more or less channels and can include thecapability to output a unique variable frequency for each of thechannels depending upon the implementation.

As previously described, the RI signal generator 16 can derive powerfrom the power supply 12 and input one or more control signals from thecontroller 14. Additional inputs can include the forward and backwardpower levels determined by the high-power amplifiers 18A-D. Based onthese inputs, the RF controller 32 can select a frequency and signal thefrequency generator 30 to output a signal indicative of the selectedfrequency. As represented pictorially in the block representing thefrequency generator 30 in FIG. 2, the selected frequency determines asinusoidal signal whose frequency ranges across a set of discretefrequencies. In one non-limiting example, a selectable bandwidth rangingfrom 2.4 GHz to 2.5 GHz can be discretized at a resolution of 1 MHzallowing for 101 unique frequency selections.

After the frequency generator 30, the signal is divided per outputchannel and directed to the phase generator 34. Each channel can beassigned a distinct phase, that is, the initial angle of a sinusoidalfunction. As represented pictorially in the block representing the perchannel phase generator 36A-D in FIG. 2, the selected phase of the RFsignal for a channel can range across a set of discrete angles. In onenon-limiting example, a selectable phase (wrapped across half a cycle ofoscillation or 180 degrees) can be discretized at a resolution of 10degrees allowing for 19 unique phase selections per channel.

Subsequent to the phase generator 34, the RF signal per channel can bedirected to the amplitude generator 38. The RF controller 32 can assigneach channel (shown in FIG. 2 with a common frequency and distinctphase) to output a distinct amplitude in the channel 40A-D. Asrepresented pictorially in the block representing the per channelamplitude generator in FIG. 2, the selected amplitude of the RF signalcan range across a set of discrete amplitudes (or power levels). In onenon-limiting example, a selectable amplitude can be discretized at aresolution of 0.5 decibels across a range of 0 to 23 decibels allowingfor 47 unique amplitude selections per channel.

The amplitude of each channel 40A-D can be controlled by one of severalmethods depending upon the implementation. For example, control of thesupply voltage of the amplitude generator 38 for each channel can resultin an output amplitude for each channel 40A-D from the RE signalgenerator 16 that is directly proportional to the desired RF signaloutput for the respective high-power amplifier 18A-D. Alternatively, theper channel output can be encoded as a pulse-width modulated signalwhere the amplitude level is encoded by the duty cycle of thepulse-width modulated signal. Yet another alternative is to coordinatethe per channel output of the power supply 12 to vary the supply voltagesupplied to each of the high-power amplifiers 18A-D to control the finalamplitude of the RF signal transmitted to the enclosed cavity 20.

As described above, the electromagnetic cooking device 10 can deliver acontrolled amount of power at multiple RF feeds 26A-D into the enclosedcavity 20. Further, by maintaining control of the amplitude, frequencyand phase of the power delivered from each RF feed 26A-D, theelectromagnetic cooking device 10 can coherently control the powerdelivered into the enclosed cavity 20. Coherent RE sources deliver powerin a controlled manner to exploit the interference properties ofelectromagnetic waves. That is, over a defined area of space andduration of time, coherent RF sources can produce stationaryinterference patterns such that the electric field is distributed in anadditive manner. Consequently, interference patterns can add to createan electromagnetic field distribution that is greater in amplitude thanany of the RF sources (i.e. constructive interference) or less than anyof the RF sources (i.e. destructive interference).

The coordination of the RF sources and characterization of the operatingenvironment (i.e. the enclosed cavity and the contents within) canenable coherent control of the electromagnetic cooking and maximize thecoupling of RF power with an object in the enclosed cavity 20. Efficienttransmission into the operating environment can require calibration ofthe RF generating procedure. As described above, in an electromagneticheating system, the power level can be controlled by many componentsincluding the voltage output from the power supply 12, the gain onstages of variable gain amplifiers including both the high-poweramplifiers 18A-D and the amplitude generator 38, the tuning frequency ofthe frequency generator 30, etc. Other factors that affect the outputpower level include the age of the components, inter-componentinteraction and component temperature.

Referring now to FIG. 3, a schematic diagram illustrating a high-poweramplifier 18 coupled to a waveguide 110 in accordance with variousaspects described herein is shown. The high-power amplifier 18 includesone or more amplification stages 100 coupled via a guiding structure 102to a circulator 104. The circulator 104 is coupled by a guidingstructure 106 to a waveguide exciter 108. The high-power amplifier 18 iselectrically coupled to the waveguide 110 by the waveguide exciter 108and mechanically coupled by an electromagnetic gasket 112.

The high-power amplifier 18 is configured such that a number ofamplification stages 100 are interconnected to amplify a radio frequencysignal from the amplifier input to the amplifier output. Theamplification stages 100 include one or more transistors configured toconvert a small change in input voltage to produce a large change inoutput voltage. Depending upon the configuration of the circuit, theamplification stages 100 can produce a current gain, a voltage gain orboth.

The output of the amplification stages 100 is coupled to the circulator104 via a guiding structure 102. The guiding structure 102 can be anyelectrical connector capable of carrying high-power radio frequencysignal including but not limited to a microstrip printed on a dielectricsubstrate of a printed circuit board. The circulator 104 is a passivemulti-port component that transmits radio frequency signals from oneport to the next where a port is a point on the circulator 104 forcoupling a radio frequency signal from one component to another. In thehigh-power amplifier 18, the circulator 104 acts as a protective deviceto isolate the amplification stages 100 from deleterious effects thatcan occur when a mismatched load reflects power.

The circulator 104 is coupled to the waveguide exciter 108 via theguiding structure 106. The high-power amplifier 18 is terminated at itsoutput by the waveguide exciter 108. The waveguide exciter 108 convertselectromagnetic energy from a first mode suitable for transmissionwithin the high-power amplifier 18 to a second mode suitable fortransmission within the waveguide 110. In this way, the waveguide 110acts as an RF feed 26A-D to convey the amplified electromagnetic signalfrom the high-power amplifier to the microwave cavity.

The electromagnetic gasket 112 provides a secure connection between thehigh-power amplifier 18 and the waveguide 110 and surrounds the portionof the waveguide exciter 108 positioned between the high-power amplifier18 and the waveguide 110. The electromagnetic gasket 112 can be formedof one or more materials useful for securing the connection between thehigh-power amplifier 18 and the waveguide 110 and providingelectromagnetic shielding at radio frequencies. Such materials caninclude, but are not limited to, silicone-based constituents filled withconductive particles such as silver or nickel.

The provision of the waveguide exciter 108 that terminates the output ofthe high-power amplifier 18 reduces the electromagnetic losses typicallyincurred at the junction of microwave devices coupled via conventionalconnectors. That is, conventional microwave devices are interconnectedvia coaxial connectors (e.g. BNC or N-type connectors) that incur RFlosses due to the additional path lengths for the connectors as well asthe losses at the coupling of the coaxial connectors. Theelectromagnetic gasket 112 augments the efficiency of the waveguideexciter 108 by shielding the waveguide exciter 108 as well as providingthe mechanical support of the coupling between the high-power amplifier18 and the waveguide 110.

Referring now to FIG. 4, a cross-sectional side view illustrating thecirculator 104 in accordance with various aspects described herein isshown. As described above, the circulator 104 is coupled to the outputof the amplification stages via the guiding structure 102. Thecirculator 104 includes a laminate 122 mounted to a metal base plate120.

Two ferrite magnets 126, 128 in axial alignment perpendicular to thelaminate 122 are secured to the laminate 122 by clips 130. The ferritemagnets 126, 128 can be any shape suitable for the circulator design,including, but not limited to a disk.

The guiding structure 102 can include a microstrip that is printed on alaminate 122. The laminate 122 is a dielectric substrate that caninclude any material suitable for the provision of insulating layers ofa printed circuit board including, but not limited to, FR-2 material orFR-4 material. The laminate 122 is positioned on the metal base plate120 that provides mechanical support to the circulator 104.Additionally, the metal base plate 120 acts as a thermal dissipatingmass and to spread heat generated by the circulator 104. The metal baseplate 120 includes a pocket 124 to house the lower ferrite magnet 128.

During the manufacturing of the circulator 104, the lower ferrite magnet128 is placed in the pocket 124 of the metal base plate 120. Thelaminate 122 and microstrip guiding structure are applied to the metalbase plate 120. The upper ferrite magnet 126 is placed above lowerferrite magnet 128 and secured to the laminate 122 by clips 130.

FIG. 5 is a top-view diagram illustrating the integrated circulator ofFIG. 4. As described, the circulator 104 includes, as part of itsmagnetic circuit, the laminate 122 of a printed circuit board as well asthe microstrip guiding structure 102 coupled to the output of theamplification stages (cf. element 100 in FIG. 3). In this way, thecirculator 104 does not include input or output pins that require asoldered connection during the manufacturing process. Conventionalsolder joints can expose the high-power amplifier to reliability issuesbecause the soldering process can result in cold-spots or bad couplings.Therefore, the circulator 104 is not a conventional discrete componentsoldered in the high-power amplifier. Instead the circulator 104 isdirectly integrated as a component of the high-power amplifier.

For the output power level at the end of the amplification stages 100 tohit a desired set-point level, the RF signal generator (cf. element 16in FIG. 1) can rely on feedback in the form of signals indicative of theforward and backward power levels or the relative phases of the radiofrequency signals conveyed to the enclosed cavity (cf. element 20 inFIG. 1). Therefore, in addition to the amplifying components foroutputting a radio frequency signal that is amplified in power withrespect to an input radio frequency signal, conventional high-poweramplifiers can include a measuring component that outputs a signalindicative of the radio frequency power transmitted and received by theamplifying component. However, by integrating such a measurementcomponent within the high-power amplifier, the output stage of ahigh-power amplifier can incur electrical losses that can reduce thepower and fidelity of the radio frequency signal output to the radiofrequency feed (cf. elements 26A-D in FIG. 1) such as a waveguide.

Referring now to FIG. 6, schematic diagram illustrating a high-poweramplifier 18 coupled to a waveguide 110 with an integrated measurementsystem 150 in accordance with various aspects described herein is shown.The integrated measurement system 150 includes probe antennas 152coupled to electronic components 154. The probe antennas 152 includeportions located within the waveguide 110 that convert radio frequencyelectromagnetic waves within the waveguide 110 into an analog electricpower signal. The probe antennas 157 can be any type of antenna usefulfor measuring radio frequency electromagnetic waves within a waveguide,including but not limited to, dipole antennas.

The electronic components 154 are coupled to the probe antennas 152 andcan include an analog-to-digital convertor (ADC) such that the outputsignal is digital and readily input to a device such as the RF signalgenerator (cf. element 16 in FIG. 1), controller (cf. element 14 inFIG. 1) or the RF controller (cf. element 32 in FIG. 1). The electroniccomponents 154 can be any component useful for the measurement of radiofrequency signals including, but not limited to, radio frequency logpower detectors that provide a direct current output voltage that islog-linear with respect to the detected radio frequency power levelwithin the waveguide 110.

The measurement system can include additional components useful forfurther characterizing the radio frequency transmissions conveyedthrough the waveguide 110. Referring now to FIG. 7, a schematic diagramillustrating a high-power radio frequency amplifier 18 coupled to awaveguide 110 with an integrated measurement system 160 that includes areflectometer 154 in accordance with various aspects described herein isshown. The integrated measurement system 160 includes probe antennas 152coupled to a reflectometer 164. The probe antennas 162 include portionslocated within the waveguide 110 that convert radio frequencyelectromagnetic waves within the waveguide 110 into an analog electricpower signal. The probe antennas 162 can be any type of antenna usefulfor measuring radio frequency electromagnetic waves within a waveguide,including but not limited to, dipole antennas.

The reflectometer 164 can include any components useful for measuringthe phase of a radio frequency signal including, but not limited to, adirectional coupler containing matched calibrated detectors or a pair ofsingle-detector couplers oriented so as to measure the electrical powerflowing in both directions within the waveguide 110. In this way, theintegrated measurement system 160 can characterize the radio frequencytransmissions according to power and phase and can be used to form anetworked description as embodied in the scattering matrix or5-parameters. In one non-limiting implementation, the reflectometer 164is a six port reflectometer configured to measure the phase of theforward and, backward radio frequency radiation within the waveguide.

The reflectometer 164 is coupled to the probe antennas 162 and caninclude an analog-to-digital convertor (ADC) such that the output signalindicative of the phase or power of the radio frequency electromagneticwave within the waveguide 110 or scattering matrix is digital andreadily input to a device such as the RF signal generator (cf. element16 in FIG. 1), controller (cf. element 14 in FIG. 1) or the RFcontroller (cf. element 32 in FIG. 1).

By characterizing the conveyed radio frequency transmissions accordingto power and phase measurements or scattering matrix, theelectromagnetic cooking device (cf. element 10 in FIG. 1) withsolid-state radio frequency sources can precisely excite an enclosedcavity (cf. element 20 in FIG. 1) by controlling the coupling factor ofthe resonant modes or standing waves that determine the heating patterntherein. That is, a solid-state electromagnetic cooking device canenergize desired heating patterns by coupling specific resonant modes tothe microwave cavity via the actuation of the radio frequency sourceswhere the heating pattern is determined by the modulus of the resonantmode. The resonant modes are a function of the cavity dimension, foodload type, food load placement and excitation condition of the multiplecoherent radio frequency sources (e.g. the operating frequency and phaseshift between the sources, etc.). The electromagnetic cooking device canbe configured to control the solid-state radio frequency sources toselect the coupling factor of the resonant modes to energize a specificheating pattern or a sequence of heating patterns over time. The heatingpatterns related to specific resonant modes can determine the evennessor unevenness of the cooking process. However, because the resonantmodes are a function of the food load type and placement, the cavitysize and excitation condition, it is not possible to have an a prioriknowledge of the resonant modes and their critical frequencies.

Therefore, the electromagnetic cooking device can be configured todetermine the resonant modes within an enclosed cavity in-situ.Referring now to FIG. 8, a schematic diagram illustrating a resonantcavity 222 coupled to two RF feeds 226A,B embodied as waveguides inaccordance with various aspects described herein is shown. The RF feeds226A,B transfer power from their respective high-power amplifiers (cf.elements 18A,B in FIG. 1) to the enclosed cavity 222. The RF feeds226A,B can be coupled to the enclosed cavity 222 in spatially separatedbut fixed physical locations. The RF feeds 226A,B can convey RFtransmissions to the enclosed cavity 222 at a selected frequency andphase where the phase shift or difference between the RF transmissionsdirectly relates to the class of symmetry of the excited resonant mode.For example activating the RF sources in an in-phase relationship (i.e.phase shift=0°) activates modes of even symmetry while activating thesources in an antiphase relationship (i.e. phase shift=) 180°) activatesmodes of odd symmetry. The symmetries determine the heating patterns inthe oven as will be described below. Although the example is given thatactivating the RF sources in an in-phase relationship (i.e. phaseshift=0°) activates modes of even symmetry while activating the sourcesin an antiphase relationship (i.e. phase shift=180°) activates modes ofodd symmetry, other phase shifts may be employed depending on thehardware architecture of the system.

In operation, the electromagnetic cooking device determines the set ofsymmetries (e.g. even or odd) for the resonant modes to be excitedwithin the cavity 222. The electromagnetic cooking device is configuredto excite the cavity 222 for a set of operating frequencies and storethe efficiency measured for each frequency. The efficiency is determinedby the useful power output divided by the total electrical powerconsumed which can be measured according to the ratio of forward powerless the backward power to forward power as in;

$\eta = \frac{{\Sigma\; P_{forward}} - {\Sigma\; P_{backward}}}{\Sigma\; P_{forward}}$The electromagnetic cooking device is configured to store the efficiencymap in memory for the excited classes of symmetries.

Referring now to FIG. 9, a graphical diagram illustrating efficiencyversus frequency for in-phase excitations 228 and antiphase excitations230 of the resonant cavity is shown. In this non-limiting illustrativeexample, the electromagnetic cooking device is configured to conduct twosets of excitations for each operating frequency and obtain twoefficiency measurements.

Referring now to FIG. 10, a diagram illustrating features of a method ofanalysis to determine the resonant modes of the cavity in accordancewith various aspects described herein is shown. The electromagneticcooking device can analyze the recorded map of efficiency (shown for thein-phase excitation 228) by modeling the response as a passband RLCcircuit in order to recognize the critical frequencies of the poles(i.e. the resonant frequencies of the resonant modes) that have beenexcited for the specific class of symmetry. For this purpose, aprocessor 250 as a physical or logical subcomponent of the controller(cf. element 14 in FIG. 1) or the RF controller (cf. element 32 in FIG.2) can be configured to identify local maxima of the efficiencyfunction. The processor 250 can implement any algorithm useful fordetermining the critical frequencies of the poles of the efficiency mapincluding, but not limited to vector fitting, magnitude vector fitting,etc. In this way, the processor 250 can determine a list of resonantfrequencies 252 for each symmetry plane.

Additionally, the processor 250 can determine a quality factor(Q-factor) based on the relative bandwidth of each determined pole. Theprocessor 250 can determine the presence of foodstuff located within thecavity based on the estimate of the Q-factor. For example, if theprocessor 250 determines that a selected resonant mode has a low factorsuch as at or below seven, the processor 250 can determine that theportions of the enclosed cavity where the excited mode has a local orglobal maximum contain foodstuff. Similarly, if the processor 250determines that a selected resonant mode has a high Q-factor such asgreater than 1000, the processor can determine that the portions of theenclosed cavity where the excited mode has a local or global maximum donot have foodstuff. The processor 250 can classify the type of foodstufflocated within the cavity based on the estimate of the Q-factor. Forexample, frozen food has a Q-factor of about 300, water has a Q-factorof about 7 and metal objects has a Q-factor of about 1000. For eachdetermined pole, the processor 250 can associate a resonant frequencyused to excite the mode and a Q-factor for determining the type offoodstuff that will be heated by the mode.

Referring now to FIG. 11, a diagram illustrating features of a method tocharacterize the resonant modes of the cavity in accordance with variousaspects described herein is shown. Building on the previously describedexample of an in-phase excitation 228 of the radio frequency feeds226A,B where a processor of the electromagnetic cooking devicedetermines a set of poles 252 indicative of the resonant modes excitablein the cavity 222, the determined poles 252A-C each correspond to aheating pattern 260A-C within the cavity 222. Recall that the heatingpattern is determined by the modulus of the resonant mode. Each heatingpattern 260A-C will have a spatial pattern with contours indicative ofuniform heating. While depicted in FIG. 11 with a binary set ofcontours, the actual heating patterns will include many contoursindicative of a continuum of heating levels. For ease of understanding,the single contour level indicates the hottest areas of the heatingpattern and demonstrates the even and odd symmetries of the resonantmodes.

Referring now to FIGS. 12A and 12B, a schematic diagram illustratingfeatures of a method to locate and classify foodstuff 300A,B positionedwithin a resonant cavity 222 in accordance with various aspectsdescribed herein is shown. Initiating an antiphase phase excitation(shown in FIG. 12A), the electromagnetic cooking device can generate aheating pattern 360A in the cavity 222 with an even symmetry where themaximum heating contours 302 do not occur in the center of the cavity222. Because a large portion 312 of the foodstuff 300A is lying within aminimum of the heating pattern 360A and only a small portion 310 of thefoodstuff 300A is lying within a maximum of the heating pattern 360A,the cavity reflections are more significant the electromagnetic responsefrom the foodstuff 300A leading to a relatively low efficiency. Incontrast, because a large portion 314 of the foodstuff 300B is lyingwithin a maximum of the heating pattern 360A, and only a small portion316 of the foodstuff 300B is lying within a minimum of the heatingpattern 360B for an in-phase excitation (FIG. 12B), the cavityreflections are minimized and the efficiency is higher than theefficiency determined during the even symmetry excitation. Therefore,the electromagnetic cooking device can determine if foodstuff is locatedin the center of the cavity 222 by comparing the efficiencies betweenthe efficiencies between an in-phase excitation and an antiphaseexcitation. To wit, a higher efficiency with in-phase excitationindicates that foodstuff is not located in the center of the cavity 222and a higher efficiency with an antiphase excitation indicates thefoodstuff is located at the center of the cavity 222. In this way, theelectromagnetic cooking device can be configured to determine thepresence of foodstuff positioned in the center of the microwave cavity222 based on the efficiency of the activated resonant modes of evensymmetry or determine the presence of foodstuff positioned remotely fromthe center of the microwave cavity 222 based on the efficiency of theactivated resonant modes of odd symmetry.

Additionally, the processor can be configured to further analyze theQ-factors according to the efficiency and symmetry of the resonant modesto detect and locate more than one type of foodstuff in the cavity 222.The processor can be configured to average the Q-factors for a subset ofthe identified resonant modes to classify a portion 310, 314 of afoodstuff 300A, 300B according to its position within the microwavecavity 222. For example, the processor can average the Q-factors of theeven symmetry modes to determine the type of foodstuff located in aportion 310 of the foodstuff 300A that intersects with the maximumheating contours 302 of the even symmetry heating patterns 360A.Similarly, the processor can average the Q-factors of the odd symmetrymodes to determine the type of foodstuff located in a portion 314 of thefoodstuff 300B that intersects with the maximum heating contours 304 ofthe odd symmetry heating patterns 360B.

Cooking applications usually require power levels in the range ofhundreds of watts, as a very common power budget for magnetron heatingsources in microwave ovens is in the range of 800-1000 W. Nonetheless,not all applications require such a high power level. For example, anapplication may require a lower power level as low as 80 W to ensurehomogeneous heating and/or a controlled process. Moreover, some cookingprocesses are destroyed or harmed if too high power levels are used(i.e. the quality of the cooking process diminishes as power levelincreases). One example of such a process is melting of butter orchocolate. Another example is raising bread, where a temperaturesuitable for yeast growth must not be exceeded for a certain amount oftime.

The use of solid-state sources allows a precise excitation of theenclosed cavity 20, 222, i.e. precise coupling to certain resonant modesto which specific heating patterns correspond. As noted above, theresonant modes are a function of the cavity dimension, food load typeand displacement and excitation condition (i.e. operating frequency andphase shift between sources in case of use of multiple coherentsources). On the other hand, with traditional non-coherent magnetronsources, such coupling is less controllable since the operatingfrequency is fixed and the phase shift relationship does not exist. Inorder to leverage the increased controllability of solid-state sourcesit is desirable to control the coupling factor of the resonant modes inorder to realize a specific heating pattern and/or a specific sequenceover time of heating patterns related to specific resonant modes inorder to achieve increased evenness and/or controlled unevenness. Suchcontrolled unevenness may be used for a zone cooking application inwhich the electric field, namely the source of heating pattern, isunbalanced to the left or to another portion of the enclosed cavity 20,222. Because the resonant modes are a function of the food load and itsdisplacement, cavity size, and excitation condition, it is not possibleto have an a priori knowledge of the resonant modes and their criticalfrequencies. It is therefore not possible to determine which resonantmodes are excited for a specific set of cavity size/food load type anddisplacement and excitation condition without having all thisinformation, for example, receiving user input at the user interface 28or having additional sensors like cameras to detect the enclosed cavity20 loading conditions and all its characteristics.

The embodiments described here relate to a method to use preclassifiedresonant modes to be activated (i.e. to which the sources transferenergy) into the enclosed cavity 20, 222 to obtain even or unevenheating of a food load. This technique may be referred to asspectromodal control as it is founded on the connection betweenabsorption spectrum and resonant modes. The theory allows homogeneousheating patterns, center-dominating heating patterns, or unbalancedpatterns. The theory stems from the observation that in an enclosedcavity 20, 222, the coupling between sources and resonant modes is afunction of the operating frequency, since such resonant modes existonly at specific discrete frequencies (the resonant frequency, criticalfrequency or so-called eigenvalues of the modes). Microwave cavities canbe represented as circuits finding an equivalent circuit that shares thesame frequency response. In view of this circuital (filter-like)representation, the resonant modes may be represented as passbandfilters centered at their critical frequencies and with a band inverselyproportional to their Q-factor. The cl-factor is related to the losses(dielectric losses that occur into the load as well as metallic lossescoming from surface currents arising into metals). The passbandrepresentation of the enclosed cavity 20, 222 is depicted in FIG. 13.The coupling of such resonant modes with respect to the operatingfrequency can be thought of as a coupling factor related to thefrequency/time factor of the excitations.

The coupling of the sources with the modes of the resonant enclosedcavity 20, 222 is a function of the excitations displacement and phaserelationship in between them (when multiple coherent sources are used)with respect to the enclosed cavity 20, 222. This second coupling factorcan be thought as related to the ‘space’ factor of the excitations. Theapplied phase shift directly relates to the class of symmetry of thetransferred resonant mode. Take as example the enclosed cavity 222depicted in FIG. 8. Activating the sources in phase relationshipactivates modes of even symmetry while activating the sources inantiphase relationship activates modes of odd symmetry. This behavior isdepicted in FIGS. 12A and 12B where FIG. 12A represents the antiphaserelationship and FIG. 12B represents the in-phase relationship. Theexplanation can be found considering the phase relationship between thetwo planes on which the two sources lay, i.e. the natural phase shiftthat the two aforementioned classes of symmetries impose on the enclosedcavity 222. For instance, every resonant mode (that composes the socalled free-response of the enclosed cavity 20) imposes specificboundary conditions on cavity walls, namely where the sources areplaced. If the enclosed cavity 20, 222 excitation is obtained throughwaveguides, a very common case for microwave ovens 10, the waveguidesshall be placed in the location and with a phase shift in between themthat matches the resonant mode that they are designed to excite. In thiscase, the enclosed cavity 20, 222, when excited (the so calledforced-response), will present an electromagnetic field configurationcorresponding to that which the resonant mode to which the excitation istargeted would have. Using such considerations, it is possible to get amap of critical frequencies and class of symmetries (spectromodalidentification). Moreover, it is possible to measure or estimate thecoupled efficiency for each identified resonant mode.

FIG. 14 is provided to show an example of an unbalanced excitation inthe enclosed cavity 222 and the resulting heating pattern. FIG. 15 isprovided to show an example of a balanced excitation in the enclosedcavity 222 and the resulting heating pattern.

Below is a list that shows the resonant modes classified according totheir symmetry and provided with their critical frequencies andefficiencies. The values shown are for purposes of example.

Symmetry 1 (even, average efficiency=79%)

-   -   Mode 1 (frequency=2.40 GHz, efficiency=70%)    -   Mode 2 (frequency=2.41 GHz, efficiency=95%)    -   Mode 3 (frequency=2.45 GHz, efficiency=80%)    -   Mode 4 (frequency=2.50 GHz, efficiency=72%)

Symmetry 2 (odd, average efficiency=79%)

-   -   Mode 1 (frequency=2.40 GHz, efficiency=69%)    -   Mode 2 (frequency=2.41 GHz, efficiency=78%)    -   Mode 3 (frequency=2.45 GHz, efficiency=90%)

The controller 14 may be configured to perform a method (400) ofactivating a sequence of preclassified resonant modes into an enclosedcavity 20, 222 to control a heating pattern therein with RF radiationfrom a plurality of RF feeds 26A-260, 226A-226B shown in FIG. 16. Theplurality of RF feeds 26A-26D, 226A-226B transfer the RF radiation intothe enclosed cavity 20, 222 and measure the forward and backward powerat the plurality of RF feeds 26A-260, 226A-226B. The method includes thesteps of selecting a heating target corresponding to an amount of energythat is to be to delivered to each symmetry plane in the enclosed cavity20, 222 based in part upon a load positioned in the enclosed cavity 20,222 (step 402); detecting asymmetries and find the optimal rotationplane (step 404); generating a heating strategy based on the heatingtarget to determine desired heating patterns, the heating strategyhaving a selected sequence of resonant modes to be excited in theenclosed cavity 20, 222 that correspond to the desired heating patterns(step 406); exciting the enclosed cavity 20, 222 with a selected set ofphasors for a set of frequencies corresponding to each resonant mode ofthe selected sequence of resonant modes (step 408) to create heatingpatterns; and monitoring the created heating patterns based on theforward and backward power measurements at the RF feeds 26A-26D,226A-226B to use closed-loop regulation to selectively modify thesequence of resonant modes into the enclosed cavity 20, 222 based on thedesired heating patterns and the created heating patterns as monitored(step 410).

A heating target is an energy set point specified according to asymmetry plane in the enclosed cavity 20, 222. In other words, a heatingtarget is the amount of energy that the microwave oven 10 is configuredto deliver to each symmetry plane. Moreover, the target set point can bespecified according to the ratio between the symmetry planes. Forexample, the target set point can be set as a 2:1 ratio for even and oddsymmetry planes where the even symmetry plane is set to receive twicethe energy as the odd symmetry plane. The heating target is configuredaccording to food load and cooking cycle requirements. For example, abalanced heating target may be configured for a reheat cycle. In anotherexample, where two separate food loads like two small glasses are placedin a symmetric fashion with respect to the cavity center on left andright halves of the oven 10, the heating target can be configured for aneven symmetry heating pattern.

The spectromodal theory ensures that sources in phase and in anti-phasegive rise to specific heating patterns that are symmetric with respectto the center of the cavity 20, 222. Thus, these patterns are suitablefor managing centered food loads, but may be very susceptible todisplacements, as highlighted in FIG. 17 where most of the energy isinjected in the right side of the food load because of the overlappingof the two patterns.

The point is that a non-centered food load introduces a rotation in thesymmetry plane that causes the system oven-load to lose its symmetricproperties. It is thus possible to compensate for this undesiredscenario, identifying the rotation of the actual symmetry plane andapplying it to the RF feeds 26A-26D, 226A-226B, hence changing theirphase relationship, as depicted in FIG. 18 where α and β are thedelta-phase between the RF feeds 26A-26D, 226A-226B.

This approach can be exploited to manage 3D displacements, i.e. on thewidth axis (as already described in FIG. 17), on the height axis and thedepth axis, by just applying the RF feeds phase-shift to the propersymmetry plane.

The outcome of selecting a heating target in step 402 is a set offrequency-phase shift excitations for each RF feed 26A-26D, 226A-226Bthat couple with one specific resonant mode. The phase-shifts appliedare the ones specific of each symmetry class, i.e. the natural phaseshift that the classes of symmetries impose on the cavity 20, 222. Theseresonant modes might then be called ‘unrotated’ or ‘nominal’ resonantmodes. The manner of identifying asymmetries and finding the optimalrotation plane (step 404) is described below.

The unrotated resonant modes selected refer to a symmetric idealscenario, hence they might be suboptimal for an asymmetric scenario.Such an asymmetrical scenario may be caused by the position of the foodload, or by the system itself (e.g., asymmetries in the manner in whichthe RE excitations are fed into the cavity). After identifying theunrotated resonant modes, the controller 14 checks whether they suit theactual system in order to find the optimal rotation that compensates foreventual asymmetries and thus provides optimized resonant modes. In somecases some of the unrotated resonant modes may turn out to not requirerotation for efficiency optimization. Accordingly, not all optimizedresonant modes are rotated. Step 402 is made up of different substeps:(1) phasors excitations; (2) excitations analysis; (3) resonant moderotation; and (4) use of power and phase sensors (vector) instead ofpower sensors (scalar).

For the first substep (phasors excitations substep (1)), after havingselected a nominal phasor, it is possible to identify a set ofexcitations for each resonant mode to be analyzed, by acting on thephase-shifts and keeping the frequency locked for that resonant mode.Specifically, for each unrotated resonant mode, the controller 14generates a set of excitations with the same frequency (of the nominalmode) and a combination of phase-shifts. The set of phases might bedefined a-priori, statically defined on run-time, or even be adaptiveaccording to different parameters. Furthermore, the phase-axis mightinclude all the phase-shifts inside the analysis range or a few samplesonly, in order to save computational time at the expense ofapproximation. The phase-shifts are not arbitrarily defined, since anexcitation related to a specific symmetry plane might couple withanother one if rotated too close to it. It is thus advantageous for thecontroller 14 to set proper bounds to the phase-axis.

The selected actuations may be stored together with their efficiencies,which can be calculated as:Efficiency=(sum of input power−sum of reflected power)/(sum of inputpower).

For each mode of each symmetry class, the map phasor/efficiency isstored, i.e. if a cavity has two ports with two possible classes and twomodes for each one has been selected, four sets of excitations will beperformed, each set with all the defined phase-shifts, thus obtainingfour sets of efficiency measurements to be further analyzed. A visualexample is shown in FIG. 19 where for each resonant mode, the controller14 performs the following:

for symmetry 1 the phasors ψ are abs(ψ)=1, arg(ψ)=e{circumflex over( )}jf0−ϕ with ϕ={−67.5°, −22.5°, 0°, 22.5°, 67.5°} for both ports; and

for symmetry 2 the phasors ψ are abs(ψ)=1, arg(ψ)=e{circumflex over( )}jf0−ϕ with ϕ={−67.5°, −22.5°, 0°, 22.5°, 67.5°} for port 1 andϕ=−180°−{−67.5°, −22.5°, 0°, 22.5°, 67.5°} for port 2.

The recorded map of efficiency is then analyzed in the second substep(excitations analysis substep (2)) in order to find the phase-shift thatoptimizes efficiency, since theoretically the efficiency vs phase curveshould follow a sinusoidal trend with a maximum on the actual symmetryplane of the system (which is 0° for symmetric ones).

Different strategies might be adopted in order to draw the efficiency vsphase curve, depending on the choices made at the previous stage. If allthe phase-axis has been considered, it is enough to scan the excitationsand find the one with the highest efficiency. Otherwise it is possibleto apply an interpolation algorithm (linear, spline etc.) or even todefine a model exploiting the a-priori knowledge about the trend of thecurve (LSQ, linear regression etc.). A visual example is shown in FIG.20.

It is also worth noticing that, since the rotation of the axis is thecombination of the phase-shifts between each pair of RF feeds 26A-26D,226A-226B and thus locking one source/source phase relationship to avalue has an impact on all the other relationships, the maximumdetection on one phase direction is correlated to all of the others.Hence, the optimal combination of the phase-shifts is not equal to thecombination of the optimum for each direction taken separately.

This leads to an optimization problem of a (nport-1)-dimensionalfunction, so for a 4-port microwave oven 10 the maximum has to besearched in a 3-dimensional plane.

For instance, given a 4-port microwave oven 10 and a phase-axis to bescanned made of four elements [−pi/4−pi/8+pi/8+pi/4] all the possiblecombinations of the phase-shifts between the ports is (provided that oneis taken as reference, so the phase does not change):(npori−1)^(nphi)=3⁴=81Hence, while in a 2-port microwave oven 10 there is only oneefficiency-phase curve to study, in a more complex system the number ofexcitations and sensing needed to find the actual optimum rotation mightdramatically increase.

For example, for a three-port system:

$\mspace{76mu}{{Sx} = {{{y\mspace{76mu}\begin{bmatrix}{s\; 11} & {s\; 12} & {s\; 13} \\{s\; 21} & {s\; 22} & {s\; 23} \\{s\; 31} & {s\; 32} & {s\; 33}\end{bmatrix}}\begin{bmatrix}{x\; 1} \\{x\; 2} \\{x\; 3}\end{bmatrix}} = \begin{bmatrix}{y\; 1} \\{y\; 2} \\{y\; 3}\end{bmatrix}}}$p(y 1) ∼ y 1 * y 1^(*) = [s 11  x 1]² + [s 12  x 2]² + [s 13  x 3]² + 2[s 11  s 12  x 1  x 2]  cos (φ x 1 − φ x 2 − φ s 11 − φ12) + 2[s 11  s 13  x 1  x 2]  cos (φ x 1 − φ x 3 − φ s 11 − φ13) + 2[s 13  s 12  x 2  x 3]  cos (φ x 2 − φ x 3 − φ s 13 − φ12)

The ‘free’ phase shifts in the previous equation (i.e. the quantities tobe controlled) are a number of three while the control variables arejust two. This stems from the fact that the given the phase shiftbetween the first and the second port (φx1−φx2) and the phase shiftbetween the first and the third port (φx1−φx3) the last phase shift(φx2−φx3) is not a control variable but satisfies the previous twoequations. That means that the number of control variables is less thanthe number of variables to be controlled and no optimal control ispossible optimizing one factor at a time.

Different approaches might be used to find the solution, such as:

-   -   solve the full problem;    -   approximate the full problem with a heuristic function;    -   consider all the sub-problems separately and combine the results        (as depicted in the FIG. 20); or    -   consider just one or a subset of the sub-problems (the most        meaningful ones with respect to a specific criterion) and solve        it/them exactly or even approximately.

Once the optimal rotation plane has been found, the resonant mode ischanged accordingly per the third substep (resonant mode rotationsubstep (3)). From reconciling the information from all the symmetryplanes it is possible to have the full picture of the resonant modesavailable in the cavity classified per class of symmetry.

Following substep (3), phase sensors are used to collect the S-matrix ofthe system (scattering matrix) in the fourth substep (use of power andphase sensors substep (4)). The scattering matrix makes it possible toperform the spectromodal excitation without actually exciting thesystem. It is possible instead to apply the equation:Sx=ywhere S is the scattering matrix of the system and x are the inputphasors and y are the output phasors and compute the input and reflectedpowers as:input power=x*conj(x)output power=y*conj(y)where conj denotes the complex conjugate.

As noted above the efficiency can be calculated as:Efficiency=(sum of input power−sum of reflected power)/(sum of inputpower).

After detecting asymmetries and finding the optimal rotation plane (step404) and thus the optimized resonant modes, the controller 14 generatesa heating strategy (step 406) to utilize the optimized resonant modes.For a given heating strategy, a selected sequence of optimized resonantmodes is stored in memory associated with controller 14. The microwaveoven 10 will be configured to execute the selected sequence by applyingthe proper phase shifts and operating frequencies of the RF channels40A-40D in order to activate the optimized resonant modes present in thelist and couple energy to thorn in the enclosed cavity 20, 222. Eachoptimized resonant mode can be activated for a specific duration oftime. For example, each mode can be excited for the same time durationor, in another example, each mode can be excited for a duration of timethat is inversely proportional to the experimentally determinedefficiency of the mode. Moreover, the sequence of optimized modes caninclude all the optimized resonant modes or just a subset that isproportional to the heating target ratio. Expanding upon the earlierexample of a target ratio of 2:1, the sequence of optimized modes caninclude twice the number of resonant modes belonging to the firstsymmetry plane with respect to the number of resonant modes belonging tothe second symmetry plane. The resonant modes belonging to a certainsymmetry can be interleaved with resonant modes belonging to the othersymmetry so as not to apply the same heating pattern for too much timethat can detrimentally affect heating performance. In another example,the sequence of optimized modes can be selected such that the sum of theinverse efficiencies of the modes belonging to a first symmetry and thesum of the inverse efficiencies of the modes belonging to a secondsymmetry are selected to satisfy the ratio target energy. In anotherexample, the microwave oven 10 can realize the energy target set pointby regulating the power output used for the RF channels 40A-40D.Collectively, the above described examples represent an open-loopoperation where the heating strategy is set and then applied. An exampleof the open-loop algorithm is depicted in FIG. 21.

After the heating strategy is generated in step 406, the controller 14excites the enclosed cavity 20, 222 with a selected set of phasors for aset of frequencies corresponding to each of the selected sequence ofresonant modes through RF feeds 26A-26D, 226A-226B (step 408).

In operation, the controller 14 can implement closed-loop regulation(step 410) by using an integrated amplifier power measurement system 150to detect the energy delivered to the load or a proxy of deliveredenergy such as the efficiency, in order to determine the net powerbalance expressed as the total input power less the total reflectedpower. The energy measurement can be integrated in an accumulatorrelative to the current symmetry plane. At specified intervals of time,the controller 14 uses closed-loop regulation to rebalance the actuationsequence of the excited modes to increase or decrease the number ofactuations for a specific symmetry plane to better achieve the requiredenergy target set point. In another example, the controller 14 can useclosed-loop regulation to adjust the power applied to the enclosedcavity 20, 222 for a specific symmetry plane or a specific mode. Anexample of the closed-loop algorithm is depicted in FIG. 22. Notice inthe example that after the rebalancing, the number of optimized resonantmodes in the first symmetry plane is reduced by one. The controller 14may also monitor the energy (or a proxy) in order to obtain feedbackabout the axis of rotation applied.

FIG. 23A is an efficiency map of one example of a food load in theenclosed cavity where the cooking appliance includes two ports. FIG. 23Bis an efficiency map of one example of a food load in the enclosedcavity where the cooking appliance includes four ports. Thus theseefficiency maps are a frequency/phase representation of two differentstates. In each map, the resonant modes are marked withsquares/triangles with respect to the symmetry plane in which they lie.The cross marker shown in FIG. 23B depicts a resonant mode that thealgorithm has filtered for some reason (for example, because it is tooclose to another one).

FIG. 24A shows an example of an efficiency map in the frequency/phasedomain where the system is mostly symmetrical and most of the resonancesare around 0° (first symmetry plane) and 180° (second symmetry plane).Such resonances would not need to be rotated. In this example, thehighest efficiency (coupling) is obtained using the nominal axis (first:0°, second 180°). FIG. 24B shows an example of an efficiency map in thefrequency/phase domain where the system is asymmetrical and most of theresonances are not around either 0° (first symmetry plane) or 180°(second symmetry plane). Such resonances may be subject to rotation. Inthis example, the highest efficiency (coupling) is obtained applyingspecific rotations to each pole. If the nominal axis (first: 0°, second180°) were used, a lower efficiency would be obtained.

An alternative to the approach described above is discussed below withreference to FIG. 25. Here, the controller 14 may be configured toperform a method (500) of activating a sequence of preclassifiedresonant modes into an enclosed cavity 20, 222 to control a heatingpattern therein with RF radiation from a plurality of RF feeds 26A-26D,226A-2268 shown in FIG. 25. The plurality of RF feeds 26A-26D, 226A-226Btransfer the RF radiation into the enclosed cavity 20, 222 and measurethe forward and backward power at the plurality of RF feeds 26A-26D,226A-226B. The method includes the steps of detecting asymmetries andfinding the optimal rotation plane (step 502); selecting a heatingtarget corresponding to an amount of energy that is to be to deliveredto each symmetry plane in the enclosed cavity 20, 222 based in part upona load positioned in the enclosed cavity 20, 222 (step 504); generatinga heating strategy based on the heating target to determine desiredheating patterns, the heating strategy having a selected sequence ofresonant modes to be transferred to the enclosed cavity 20, 222 thatcorrespond to the desired heating patterns (step 506); exciting theenclosed cavity 20, 222 with a selected set of phasors for a set offrequencies corresponding to each resonant mode of the selected sequenceof resonant modes (step 508) to create heating patterns; and monitoringthe created heating patterns based on the forward and backward powermeasurements at the RF feeds 26A-26D, 226A-226B to use closed-loopregulation to selectively modify the sequence of resonant modes into theenclosed cavity 20, 222 based on the desired heating patterns and thecreated heating patterns as monitored (step 510).

In method 500, the steps of detecting asymmetries and finding theoptimal rotation plane (step 502) and selecting a heating target (step504) are performed in a reversed order than in method 400 describedabove with respect to FIG. 16. In addition, the details of these twosteps are different. Specifically, in step 402, the first, second, andthird substeps (phasors excitations substep (1), excitations analysissubstep (2), and resonant mode rotation substep (3)) are now performedin the asymmetry detecting step 502 rather than the heating targetselection step 504. To find optimum rotations, the controller 14generates a preselected set of excitations to find frequenciesrepresenting unrotated resonant modes and then generates excitations ina small region close to those frequencies representing resonant modeswhile shifting the phases and measuring the resulting efficiencies. If aspecific phase at a frequency leads to an increase in efficiency, theoptimized resonant mode is the phase-shifted one, and the rotation isthe phase shift. Thus, in step 502, substep (1), the controller 14 firstexcites the cavity with a plurality of pre-selected frequencies toidentify unrotated resonant modes and then identifies a set ofexcitations for each unrotated resonant mode to be analyzed by acting ona plurality of phase-shifts and keeping the frequency locked for thatresonant mode. Specifically, for each unrotated resonant mode, thecontroller 14 generates a set of excitations with the same frequency (ofthe nominal mode) and a combination of phase-shifts. The set of phasesmight be defined a-priori, statically defined on run-time, or even beadaptive according to different parameters. Furthermore, the phase-axismight include all the phase-shifts inside the analysis range or a fewsamples only, in order to save computational time at the expense ofapproximation. The phase-shifts are not arbitrarily defined, since anexcitation related to a specific symmetry plane might couple withanother one if rotated too close to it. It is thus advantageous for thecontroller 14 to set proper bounds to the phase-axis.

The selected actuations may be stored together with their efficiencies.For each mode of each symmetry class, the map phasor/efficiency isstored, i.e. if a cavity has two ports with two possible classes and twomodes for each one has been selected, four sets of excitations will beperformed, each set with all the defined phase-shifts, thus obtainingfour sets of efficiency measurements to be further analyzed.

The recorded map of efficiency is then analyzed in the second substep(excitations analysis substep (2)) in order to find the phase-shift thatoptimizes efficiency, since theoretically the efficiency vs. phase curveshould follow a sinusoidal trend with a maximum on the actual symmetryplane of the system.

Once the optimal rotation plane has been found, the resonant mode ischanged accordingly per the third substep (resonant mode rotationsubstep (3)). From reconciling the information from all the symmetryplanes it is possible to have the full picture of the resonant modesavailable in the cavity classified per class of symmetry. Additionaldetails of substeps (1)-(3) are described above with respect to FIG. 16.

In step 504, a heating target is then selected corresponding to anamount of energy that is to be to delivered to each symmetry plane inthe enclosed cavity based in part upon the food load positioned in theenclosed cavity where the heating target includes a plurality ofresonant modes that are rotated using the selected rotations in thepreceding step 502. Step 502 thus includes substep (4) of step 402described above. When selecting a heating target, the controller 14 isfurther configured to select the heating target according to food loadand cooking cycle requirements.

Following step 504, the controller 14 performs steps 506-510, whichcorrespond to steps 406-410 of FIG. 16. Insofar as these steps are thesame, the details of steps 506-510 are not provided. Instead, thedescription of steps 406-410 above is incorporated herein by reference.

For purposes of this disclosure, the term “coupled” (in all of itsforms, couple, coupling, coupled, etc.) generally means the joining ofcomponents (electrical or mechanical) directly or indirectly to oneanother. Such joining may be stationary in nature or movable in nature.Such joining may be achieved with the two components (electrical ormechanical) and any additional intermediate members being integrallyformed as a single unitary body with one another or with the twocomponents. Such joining may be permanent in nature or may be removableor releasable in nature unless otherwise stated.

It is also important to note that the construction and arrangement ofthe elements of the device as shown in the exemplary embodiments isillustrative only. Although only a few embodiments of the presentinnovations have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multiple partsor elements shown as multiple parts may be integrally formed, theoperation of the interfaces may be reversed or otherwise varied, thelength or width of the structures and/or members or connector or otherelements of the system may be varied, the nature or number of adjustmentpositions provided between the elements may be varied. It should benoted that the elements and/or assemblies of the system may beconstructed from any of a wide variety of materials that providesufficient strength or durability, in any of a wide variety of colors,textures, and combinations. Accordingly, all such modifications areintended to be included within the scope of the present innovations.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions, and arrangement of the desired andother exemplary embodiments without departing from the spirit of thepresent innovations.

It will be understood that any described processes or steps withindescribed processes may be combined with other disclosed processes orsteps to form structures within the scope of the present device. Theexemplary structures and processes disclosed herein are for illustrativepurposes and are not to be construed as limiting.

It is also to be understood that variations and modifications can bemade on the aforementioned structures and methods without departing fromthe concepts of the present device, and further it is to be understoodthat such concepts are intended to be covered by the following claimsunless these claims by their language expressly state otherwise.

The above description is considered that of the illustrated embodimentsonly. Modifications of the device will occur to those skilled in the artand to those who make or use the device. Therefore, it is understoodthat the embodiments shown in the drawings and described above is merelyfor illustrative purposes and not intended to limit the scope of thedevice, which is defined by the following claims as interpretedaccording to the principles of patent law, including the Doctrine ofEquivalents.

What is claimed is:
 1. An electromagnetic cooking device comprising: anenclosed cavity in which a food load is placed; a plurality of RF feedsconfigured to introduce electromagnetic radiation into the enclosedcavity to heat up and prepare the food load, the plurality of RF feedsconfigured to allow measurement of forward and backward power at theplurality of RF feeds; and a controller configured to: detectasymmetries relative to a center of the enclosed cavity and selectrotations that compensate for the detected asymmetries; select a heatingtarget corresponding to an amount of energy that is to be to deliveredto each symmetry plane in the enclosed cavity based in part upon thefood load positioned in the enclosed cavity where the heating targetincludes a plurality of resonant modes that are rotated using theselected rotations in the preceding step; generate a heating strategybased on the heating target to determine a sequence of desired heatingpatterns, the heating strategy having a selected sequence of theplurality of resonant modes to be excited in the enclosed cavity thatcorresponds to the sequence of desired heating patterns; cause the RFfeeds to output a radio frequency signal of a selected frequency, aselected phase value and a selected power level to thereby excite theenclosed cavity with a selected set of phasors for a set of frequenciescorresponding to each resonant mode of the selected sequence of resonantmodes to create heating patterns; and monitor the created heatingpatterns based on the forward and backward power measurements at the RFfeeds to use closed-loop regulation to selectively modify the sequenceof resonant modes into the enclosed cavity based on the desired heatingpatterns as monitored.
 2. The cooking device of claim 1, wherein, whendetecting asymmetries of the system and selecting rotations, thecontroller is further configured to: identify rotations that compensatefor the detected asymmetries by generating a set of excitations thatapply a combination of phase shifts and determining an electricalefficiency for each excitation so as to determine the phase shifts thatoptimize the electrical efficiency.
 3. The cooking device of claim 1,wherein, when monitoring the created heating patterns, the controller isfurther configured to: collect forward and reflected power measurementsfor the selected set of phasors; and determine an absorption spectrumfor the selected set of phasors.
 4. The cooking device of claim 1,wherein, when monitoring the created heating patterns, the controller isfurther configured to: identify and classify the resonant modes of theenclosed cavity; correlate an absorption spectrum and the resonant modesin the enclosed cavity; and access a stored map of critical frequenciesand class of symmetries where a symmetry of the resonant mode determinesthe heating pattern in the enclosed cavity.
 5. The cooking device ofclaim 1, wherein, when monitoring the created heating patterns, thecontroller receives from an integrated amplifier power measurementsystem, a detected energy delivered to the load or a proxy of deliveredenergy such as the efficiency, in order to determine a net power balanceexpressed as a total input power less a total reflected power.
 6. Thecooking device of claim 1, wherein, when selecting a heating target, thecontroller is further configured to select the heating target accordingto food load and cooking cycle requirements.
 7. The cooking device ofclaim 1, wherein, when generating a heating strategy, the controller isfurther configured to determine a specific duration of time for eachresonant mode to be activated in the sequence of resonant modes.
 8. Thecooking device of claim 1, wherein, when generating a heating strategy,the controller is further configured to interleave resonant modesbelonging to a certain symmetry with resonant modes belonging to anothersymmetry.
 9. The cooking device of claim 1, wherein, when generating aheating strategy, the controller is further configured to select asequence of modes such that a sum of inverse efficiencies of modesbelonging to a first symmetry and a sum of inverse efficiencies of modesbelonging to a second symmetry satisfy a ratio target energy.
 10. Thecooking device of claim 1, and further comprising: a set of high-powerRF amplifiers coupled to the plurality of RF feeds, each high-poweramplifier comprising at least one amplifying stage configured to outputa signal that is amplified in power with respect to an input RF signal;and a signal generator coupled to the set of high-power RF amplifiersfor generating the input RF signal; wherein the controller causes the RFfeeds to output a radio frequency signal of a selected frequency, aselected phase value and a selected power level by causing the signalgenerator and selected ones of the set of high-power amplifiers tooutput a radio frequency signal of a selected frequency, a selectedphase value and a selected power level, wherein the selected frequencyis selected from a set of frequencies in a bandwidth of radio frequencyelectromagnetic waves, the selected phase value is selected from a setof phase values of radio frequency electromagnetic waves, and theselected power level is selected from a set of power levels.
 11. Thecooking device of claim 1, wherein each of the plurality of RF feedsincludes a waveguide coupled at one end to one of the high-power RFamplifiers and coupled at the other end to the enclosed cavity.
 12. Thecooking device of claim 1, wherein each of the plurality of RF feedsincludes an integrated measurement system configured to output a digitalsignal indicative of the RF signal conveyed within the waveguide.
 13. Amethod of activating a sequence of preclassified resonant modes into anenclosed cavity in which a food load is placed to control a heatingpattern therein with RF radiation from a plurality of RF feeds, wherethe plurality of RF feeds transfer the RF radiation into the enclosedcavity and measure the forward and backward power at the plurality of RFfeeds, the method comprising: detecting asymmetries relative to a centerof the enclosed cavity and select rotations that compensate for thedetected asymmetries; selecting a heating target corresponding to anamount of energy that is to be to delivered to each symmetry plane inthe enclosed cavity based in part upon the food load positioned in theenclosed cavity where the heating target includes a plurality ofresonant modes that are rotated using the selected rotations in thepreceding step; generating a heating strategy based on the heatingtarget and the selected rotations to determine a sequence of desiredheating patterns, the heating strategy having a selected sequence of theplurality of optimized resonant modes to be excited in the enclosedcavity that corresponds to the sequence of desired heating patterns;exciting the enclosed cavity with a selected set of phasors for a set offrequencies corresponding to each resonant mode of the selected sequenceof optimized resonant modes to create heating patterns; and monitoringthe created heating patterns based on the forward and backward powermeasurements at the RF feeds to use closed-loop regulation toselectively modify the sequence of optimized resonant modes into theenclosed cavity based on the desired heating patterns as monitored. 14.The method of claim 13, wherein the step of detecting asymmetries of thefood load and selecting rotations, comprises: identifying rotations thatcompensate for the detected asymmetries by generating a set ofexcitations that apply a combination of phase shifts and determining anelectrical efficiency for each excitation so as to determine the phaseshifts that optimize the electrical efficiency.
 15. The method of claim13, wherein the step of monitoring includes: collecting forward andreflected power measurements for the selected set of phasors; anddetermining an absorption spectrum for the selected set of phasors. 16.The method of claim 13, wherein the step of monitoring includes:identifying and classifying the resonant modes of the enclosed cavity;correlating an absorption spectrum and the resonant modes in theenclosed cavity; accessing a stored map of critical frequencies andclass of symmetries where a symmetry of the resonant mode determines theheating pattern in the enclosed cavity.
 17. The method of claim 13,wherein the step of monitoring includes using an integrated amplifierpower measurement system to detect the energy delivered to the load or aproxy of delivered energy such as the efficiency, in order to determinea net power balance expressed as a total input power less a totalreflected power.
 18. The method of claim 13, wherein the step ofselecting a heating target comprises selecting the heating targetaccording to food load and cooking cycle requirements.
 19. The method ofclaim 13, wherein the step of generating a heating strategy includesdetermining a specific duration of time for each resonant mode to beactivated in the sequence of resonant modes.
 20. The method of claim 13,wherein the step of generating a heating strategy includes interleavingresonant modes belonging to a certain symmetry with resonant modesbelonging to another symmetry.